The present invention relates a method and apparatus for removing warps or surface irregularities from phonograph records, and more particularly, records made of polyvinyl materials such as used in modern, long-playing, high fidelity records. Such records are often delivered by a supplier to the end user in a moderately to severely warped condition. Such conditions generally result from a combination of factors, including inadequately controlled manufacturing processes, temperature variations and stresses during shipping and storage, and inadequate storage facilities or conditions maintained by the supplier. Once in the hands of the end user or consumer, such planar records are subject to further warpage and deterioration with usage and due to further inadequate storage facilities and conditions.
Warpage of modern polyvinyl records presents problems which did not exist with the older type, less pliable 78 RPM records. Because modern, sophisticated, high fidelity sound reproduction equipment is capable of following and reproducing all variations on a record, including warps, even very small non-planar variations in the surface of a record adversely affect the fidelity of the reproduced sound. In addition to the loss of fidelity in the sound reproduction, subsonic signals can be generated by even a slightly warped record which can drive a hi-fi power amplifier into a clipping region further distorting fidelity and potentially causing damage to loud-speakers. Extreme warps can render a record unplayable. Even with turntable, tonearm and cartridge combinations of extreme sophistication, unacceptable quality sound reproduction occurs with record warpage.
Subsonic signals are also reported to be capable of causing adverse physiological effects known generically as flicker vertigo, which can produce spatial disorientation or blackout if the signals are of sufficient strength and duration. Reportedly, even minute warps in a record can generate such subsonic signals through an appropriate amplifing system.
Although U.S. Pat. No. 2,388,127 discloses an apparatus for flattening disc records, it is totally inapplicable to modern records since, for example, it utilizes two superposed plates which engage the playing surface of the record. Although this technique would be appropriate for an earlier generation record it would severely damage a modern polyvinyl record.